V-22 Osprey

Fuel System

The V-22's fuel system is integrated into the wings and fuselage. The basic configuration consists of five tanks, the two feed tanks, two forward sponson tanks and the right aft sponson tank. This is the standard MV-22 configuration. The CV-22 adds four additional tanks in each wing. Both variants can carry additional auxiliary tanks in the cabin for self-deployment or ferry missions. The following table lists the number and capacity of each tank.

Engine fuel is supplied by the left and right feed tanks to the adjacent engine. All other tanks transfer to these feed tanks and can also be cross-fed to the opposite feed tank. Fuel transfer operations are automatic, although some functions can be controlled by the pilot. The automatic transfer sequence empties the internal cabin tanks first if they are installed, the right aft sponson next, the wing tanks next and then both the left and right forward sponson tanks.

The V-22 fuel system is capable of supplying 30 minutes of fuel from the feed tanks to the engines with a complete loss of power to the Fuel Management Gauging System (FMGS).The FMUs are the Fuel Management Units. There are two non-redundant FMUs: # 1 is responsible for the left side of the aircraft, and #2 for the right side. They are, in essence, the "brains" of the fuel system, managing the tanks, sensors and valves for their respective sides of the aircraft. In addition to managing the flow of fuel, they also provide data as to how much fuel remains. If one FMU fails, the other has an estimation routine, which allows it to estimate the amount of fuel remaining on the other side of the aircraft. During one-engine-inoperative (OEI) operation, the fuel in the opposite feed cell can be transferred to the side with the operating engine. The cross-transfer valve is controlled automatically by the FMUs, but the control may be overridden at the operator's discretion.

Safety was a major concern in the fuel system design. An onboard inert gas generating system (OBIGGS) supplies nitrogen-rich air to the wing and sponson tanks as fuel is depleted. The inert gas displaces fuel vapor and reduces the possibility of fire. All tanks are self-sealing to a 12.7 mm AP threat and meet a drop test requirement of 65 feet when filled with water. Self-sealing breakaway valves are located at each line-to-tank connection. For ballistic and crash protection, a suction system is used for normal sponson tank to feed tank transfers.

The bladder-type wing fuel cells are crashworthy and (except for the access covers) fully self-sealing to fully tumbled .50 cal. APM2 projectiles. The transfer lines and primary feed lines are not self-sealing. These lines contain fuel and, if severed, the fuel could feed a fire. However, they are designed to be under suction (negative pressure) and, normally, the fuel will be sucked clear. Ballistic penetration of one transfer line will result in loss of fuel transfer capability to one feed cell. Fuel remaining in the wing auxiliary and sponson tanks on the side where the transfer line is severed becomes unusable to either engine.

Bladder-type fuel cells in the sponsons and wing auxiliary cells are crashworthy and partially self-sealing in accordance with MIL-T-27422, Type 1, protection Level B. Material used in these cells is self-sealing to .50 cal. APM2 fully-tumbled projectiles. The wing auxiliary cells contain self-sealing material in the lower one-third of the cell. The sponson cells currently contain self-sealing material on the lower one-third of the cell and full self-sealing on the inboard, forward and aft vertical walls.

All fuel cell ullages are protected from explosion due to ballistic impacts by use of onboard inert gas generating system (OBIGGS), which provides inerting nitrogen-enriched gas to the feed cells and sponsons. The enriched nitrogen environment displaces the air in the cells through the vent system, thereby reducing vulnerability to fire and explosions after ballistic impacts and crash landings. The OBIGGS provides the nitrogen-enriched gas at a pressure of 1-2 psig during the entire V-22 mission. Dry bay fire protection in the wing and sponson is also provided.

Voids between the engine feed tank and surrounding structure are filled with ballistic foam between stringers above and below the tank, and between the feed tank and adjacent ribs. Aluminum oxide powder-filled panels are bonded to the forward face of the forward spar sections that lie in front of the engine feed tanks. These panels are designed to suppress incendiary flash and provide fire protection in the small dry bay between the forward spar and the leading edge of the wing skin. Detector/suppressor units provide dry bay protection in the aft wing cove area and in the dry bays immediately inboard and outboard of the engine feed tank. These units employ non-discriminating detectors (e.g., no differentiation between an incendiary flash and a fire) and solid chemical gas generator suppressors, which use non-ozone depleting agents.

Fire protection in the sponson dry bays is accomplished with the use of approximately 0.8 inches of rigid foam sandwiched between each fuel cell and the stiffeners of the forward and aft bulkhead. This provides protection from fire in voids, as well as the adjacent dry bay. This foam is also being reevaluated. Rigid foam (3 inches) is also installed under the cabin floor, next to the fuel cell structure.

The V-22 can refuel through a single point ground pressure refueling system. This is managed from a control panel in the aft left sponson. The Osprey can be fitted with an aerial refueling probe to provide in-flight refueling from properly equipped tanker aircraft. This greatly extends the V-22 useful range. It can also be refuelded using only gravity through the forward left sponson tank. The sponson tank boost pumps transfers fuel to all other tanks. The V-22 can defuel using suction or gravity drain. Fuel can also be dumped overboard during emergency situation at a rate of 800 lbs/min. All fuel can be dumped except for the feed tanks.